Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session M15: Few-Body Systems |
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Sponsoring Units: GFB Chair: Rocco Schiavilla, Thomas Jefferson National Accelerator Facility Room: Key 11 |
Sunday, April 12, 2015 3:30PM - 3:42PM |
M15.00001: Compton Scattering from Deuterium and the Electromagnetic Polarizabilities of the Neutron Gerald Feldman The electric and magnetic polarizabilities of the neutron are still relatively uncertain, as compared to those values for the proton. To address this problem, a multi-institutional collaboration has conducted a program of elastic Compton scattering experiments on deuterium at the MAX IV Laboratory in Lund, Sweden using tagged photons spanning the energy range $E_{\mathrm{\gamma }}=$ 65-115 MeV. We assembled at one laboratory, for the first time, three of the world's largest NaI detectors (each with $\Delta E$/$E\sim $ 2{\%}) and measured elastic Compton scattering cross sections at lab angles of $\theta_{\mathrm{\gamma }}=$ 60\textordmasculine , 120\textordmasculine and 150\textordmasculine . This effectively doubles the world's set of elastic Compton scattering data from deuterium and provides valuable input for chiral effective field theory ($\chi $EFT) calculations. The absolute normalization of the current data was rigorously checked via separate measurements of elastic Compton scattering on carbon, which can be compared with precise values in the literature. These new deuterium data overlap previous measurements and extend them by 20 MeV to higher energies. Based on $\chi $EFT fits to the expanded world data set, new values for the neutron electric and magnetic polarizabilities have been obtained with greater accuracy than previously achieved, decreasing the statistical error by more than 30{\%}. [Preview Abstract] |
Sunday, April 12, 2015 3:42PM - 3:54PM |
M15.00002: A New High-Accuracy Analysis of Compton Scattering in Chiral EFT: Neutron Polarisabilities Harald W. Griesshammer, Judith A. McGovern, Daniel R. Phillips Low-energy Compton scattering tests the symmetries and interaction strengths of a target's internal degrees of freedom in the electric and magnetic fields of a real, external photon. In the single-nucleon sector, information is often compressed into the static scalar dipole polarisabilities which are experimentally not directly accessible but encode information on the pion cloud and the $\Delta(1232)$ excitation. The interaction of the photon with the charged pion-exchange also provides a conceptually clean probe of few-nucleon binding. After demonstrating the statistical consistency of the world's $\gamma$d dataset including the new data from the MAX-IV collaboration described in the preceding talk, we present a new extraction of the neutron polarisabilities in Chiral Effective Field Theory: $\alpha_n=[11.55\pm1.25(\rm{stat})\pm0.2(\rm{BSR})\pm0.8(\rm{th})]$ and $\beta_n=[3.65\mp1.25(\rm{stat})\pm0.2(\rm{BSR})\mp0.8(\rm{th})]$, in $10^{-4}$ fm${}^3$, with $\chi^2=45.2$ for $44$ degrees of freedom. The new data reduced the statistical uncertainties by $30$\%. We discuss data accuracy and consistency, the role of the $\Delta(1232)$, and an estimate of residual theoretical uncertainties. Within statistical and systematic errors, proton and neutron polarisabilities remain identical. [Preview Abstract] |
Sunday, April 12, 2015 3:54PM - 4:06PM |
M15.00003: Hadron electric polarizability from lattice QCD Andrei Alexandru, Michael Lujan, Walter Freeman, Frank Lee Electric polarizability measures the ability of the electric field to deform a particle. Experimentally, electric and magnetic polarizabilities can be measured in Compton scattering experiments. To compute these quantities theoretically we need to understand the internal structure of the scatterer and the dynamics of its constituents. For hadrons - bound stated of quarks and gluons - this is a very difficult problem. Lattice QCD can be used to compute the polarizabilities directly in terms of quark and gluons degrees of freedom. In this talk we focus on the neutron. We present results for the electric polarizability for two different quark masses, light enough to connect to chiral perturbation theory. These are currently the lightest quark masses used in lattice QCD polarizability studies. For each pion mass we compute the polarizability at four different volumes and perform an infinite volume extrapolation. For one ensemble, we also discuss the effect of turning on the coupling between the background field and the sea quarks. We compare our results to chiral perturbation theory expectations. [Preview Abstract] |
Sunday, April 12, 2015 4:06PM - 4:18PM |
M15.00004: Quantum Monte Carlo calculations of electromagnetic transitions and magnetic radii of light nuclei with two-body $\chi$EFT currents Saori Pastore, Rocco Schiavilla, Robert Wiringa, Steven Pieper We present a number of ab initio Quantum Monte Carlo calculations of electromagnetic observables for $A\le 10$ nuclei, which account for two-body effects due to the coupling of external photons with pairs of interacting nucleons. We use the realistic Argonne v18 two-nucleon and Illinois-7 three-nucleon potentials to generate the nuclear wave functions, and chiral effective field theory with pions and nucleons to construct the two-body electromagnetic current operators. Emphasis is on recent calculations of magnetic radii of light nuclei. [Preview Abstract] |
Sunday, April 12, 2015 4:18PM - 4:30PM |
M15.00005: Measurement of the Double Polarization Observables $C_x$ and $C_z$ for $\Lambda n$ Final-state Interactions in $\overrightarrow{\gamma} d\rightarrow K^+ \overrightarrow{\Lambda} n$ Tongtong Cao Building a comprehensive picture of the strong interaction is the goal of modern nuclear physics. While considerable progress has been made in the understanding of the nucleon-nucleon (NN) interaction, we are still far from a complete understanding of the hyperon-nucleon (YN) interaction, which plays a key role in hypernuclear matter and neutron stars. For the YN potential, some parameters can be obtained from the NN potential by using SU(3) symmetry. However, other parameters cannot be obtained from the NN potential due to broken SU(3) and must be obtained from fits to experimental data. One can access the dynamics of the YN interaction by studying nuclear reactions in which hyperons are produced. In this talk we present preliminary results for the polarization transfers $C_x$ and $C_z$ from the photon to the hyperon for final-state interactions in $\overrightarrow{\gamma} d\rightarrow K^+ \overrightarrow{\Lambda} n$ and discuss their dependence on kinematic variables. We use data taken with the CLAS detector at Thomas Jefferson National Accelerator Facility. Our results are the first ever obtained for $C_x$ and $C_z$ and will provide stringent constraints on the theoretical models of the YN potential. This work is funded in part by the U.S. NSF under grant PHY-125782. [Preview Abstract] |
Sunday, April 12, 2015 4:30PM - 4:42PM |
M15.00006: Study of double-antikaonic $K^{-} K^{-} p$ cluster: numerical benchmarks Sh.M. Tsiklauri, R.Ya. Kezerashvili, I. Filikhin, V.M. Suslov, B. Vlahovic A double-antikaonic cluster $K^{-} K^{-} p$ is studied using two different methods: the method of hyperspherical functions in momentum representation and method of the Faddeev equations in configuration space. Binding energy and width of the system $K^{-} K^{-} p$ is calculated by employing the energy dependent chiral \textit{KN} interaction, as well as a phenomenological KN potential. The ground state energy shows very strong dependence on the antikaon-nucleon potential, as well as the extreme sensitivity of the width to the $K^{-} p$ potential. The energy of the ground state calculated for the energy independent \textit{KN} interaction is more than three times bigger than one obtained for the energy dependent chiral \textit{KN} potential. The energies of the ground state obtained in both methods are in a reasonable agreement. Cluster approach for the Faddeev equations was applied to demonstrate contributions of the configurations ($K^{-} K^{-}$) $+ p$ and ($K^{-}p$)$^{singlet} + K^-$ , ($K^{-} p$)$^{triplet} + K^{-}$ to total wave function of the system. The comparison of our results with calculations within variational methods and the Faddeev equations in momentum representation is presented. [Preview Abstract] |
Sunday, April 12, 2015 4:42PM - 4:54PM |
M15.00007: Quasi-bound state in $K^{-} pp$ system: numerical benchmarks R. Ya. Kezerashvili, Sh. M. Tsiklauri, I. Filikhin, V.M. Suslov, B. Vlahovic Calculations for a deeply bound state and width of the kaonic three-body $K^{-} pp$ system are presented using realistic nucleon-nucleon potentials and the energy dependent chiral \textit{KN} interaction, as well as a phenomenological energy independent \textit{KN} potential. Two totally different methods, one the method of hyperspherical functions in momentum representation and the other solving the Faddeev equations in configuration space, are used to study the ground state energy of the system and to compare these two different approaches. The Argonne V14 and Maliet and Tjon potentials for the \textit{NN}-interaction, and the energy dependent chiral \textit{KN} interaction, and an energy independent phenomenological \textit{KN} potential for description of the kaon-nucleon interaction were used. The results of calculations obtained by both methods are in a reasonable agreement. The ground state energy not sensitive to the \textit{NN} interaction, however shows very strong dependence on the kaon-nucleon potential. The energy of the ground state, as well as the width calculated for the energy independent \textit{KN} interaction are more than twice bigger than for the energy dependent chiral \textit{KN} potential. The theoretical discrepancies in the binding energy and width for the $K^{-} pp$ system related to the different \textit{NN} and \textit{KN } interactions are discussed. [Preview Abstract] |
Sunday, April 12, 2015 4:54PM - 5:06PM |
M15.00008: Universality and the Coulomb dissociation of two-neutron halos Danel Phillips, Bijaya Acharya, Philipp Hagen, Hans-Werner Hammer In the limit of large two-body s-wave scattering length few-body systems display {\it universality}: their properties are independent of the details of interactions. Such universality is present in halo nuclei where two neutrons orbit a tightly bound nuclear core. There, the neutron-neutron (nn) scattering length is much larger than the range of the nn force, and, if the neutron-core scattering length obeys $|a|\gg R$, the system can be described by an effective field theory (EFT) based on this separation of scales. In this ``Halo EFT" the degrees of freedom are the neutrons and the core; core structure is included at higher order in the EFT. At leading order (LO) in the $R/a$ expansion one three-body datum is needed as input to obtain renormalized predictions for core-n-n observables. Here we take that datum to be the two-neutron separation energy, $S_{2n}$, of a 2n-halo nucleus. At LO all properties of a 2n-halo are functions of $S_{2n}$ and the two-body scattering lengths. In particular, its Coulomb dissociation spectrum is a universal function of these parameters. We compute that function, and compare it to experimental data from $^{11}$Li. We also discuss how measurements of the Coulomb dissociation of $^{22}$C can constrain both its $S_{2n}$ and properties of $^{21}$C. [Preview Abstract] |
Sunday, April 12, 2015 5:06PM - 5:18PM |
M15.00009: The Non-Perturbative Scalar Yukawa Theory on the Light Front Yang Li, Vladimir Karmanov, Pieter Maris, James Vary We present a non-perturbative calculation of the scalar Yukawa model in light-front dynamics with a Fock sector dependent renormalization. The Fock space is truncated to four particles and then the \textit{ab initio} Hamiltonian approach is applied. We compute the electromagnetic form factor and compare it with the results obtained from the lower Fock sector truncations. We find that the one- and two-body contributions dominate the Fock space even in the non-perturbative region. However, the four-body contribution exceeds the three-body one as the coupling constant increases. Nevertheless, the form factor shows a good converge as the number of constituent bosons increases. [Preview Abstract] |
Sunday, April 12, 2015 5:18PM - 5:30PM |
M15.00010: Phase Structure of the T-matrix and Multichannel Unitary Isobar Model S. Razavi, K. Nakayama By exploiting the full phase structure of the meson-baryon coupled channels reaction amplitude--here including also the photon-baryon channel--an isobar model is constructed which fulfills automatically the unitarity and analyticity conditions of the S-matrix, in addition to gauge invariance in the case of photoproduction. In particular, it is shown that the unitarity of the (resonance) pole amplitude arises from the dressing mechanism inherent in the basic T-matrix equation, requiring no extra unitarity condition on the pole amplitude as is the case in earlier works on isobar models. As an example, the present model is applied in the description of the meson-nucleon reactions including the $\pi N$, $\eta N$, $\sigma N$, $\rho N$ and $\pi\Delta$ channels. The latter three account effectively for the $\pi\pi N$ channel. [Preview Abstract] |
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